Superregenerative receiver



Feb. 4, 1947. A WHEELER 2,415,317

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Fraquenyw Patenied Feb. 4, 1947 UNITED STATES'PATENT orrice SUPERREGENERATIVE RECEIVER Harold A. Wheeler, Great Neck, N. Y., assignor, by mesne assignments, to Hazcltine Research, Inc., Chicago, 111., a corporation of Illinois Application April 14, 1944, Serial No. 531,029

' 9 Claims.

This invention is directed to a superregenerative receiver for receiving modulated carrier-frequency wave signals/ I A superregenerative receiver, as is well understood in the art, comprises a regenerative oscillatory circuit which is periodically quenched at a frequency much less than that of the generated oscillations. Also, for optimum reception of modulated carrier-frequency wave signals, it is preferable that the quench frequency be much greater than the highest modulation frequency of the received signal desired to be translated. Such a receiver is characterized by a high gain and the oscillations generated in succeeding quench cycles vary in accordance with the amplitude of the exciting signal which initiates the oscillamany installations the described receiver arrangement is satisfactory but, in others, the signal components introduced into the detected output signal by virtue of the quenching action are undesirable.

Consider, for example, an installation in which it is desirable to derive modulation components of a received modulated carrier-frequency wave signal with as high fidelity as possible. This may be necessary in a case where the output signal of the receiver is displayed on the screen of a cathode-ray oscilloscope to enable the intelligence represented by modulation of the received signal to be obtained by visual inspection. In such a case, those signal components of the detected output signal which result from the quenching action are present in the oscilloscope picture and cause the picture to be an unfaithful reproduction of the modulation components of the received signal.

Arrangements have been proposed for reducing the effect of the undesired quench-frequency signal componentsof the receiver output signal.

In one arrangement a small shuntconnected condenser is included in the load circuit of the detector system. Such a condenser hasa gradually sloping frequency-response characteristic and fails to suppress sufficiently the low-order undesired quench-frequency signal components. In other arrangements a large shunt-connected condenser has been provided in the detector system .to suppress all of the undesired quench-frequency components. Such a condenser has a sharply dropping frequency-response characteristic and undesirably attenuates the high-frequency modulation signal components of the received signal. Finally, it has been proposed to utilize a low-pass filter network having a sharp cutoff at a frequency corresponding to about half the quench frequency-and a substantially uniform amplitude of response over its pass band.

This latter arrangement is ideal from the standpoint of signal selection. Howeverfsuch a filter network inherently has a nonuniform-frequency time-delay characteristic which results in undesirable distortion of the detected modulation signal components.

It is an object of the invention, therefore, to provide an improved superregenerative receiver for receiving modulated carrier-frequency wave signals and which avoids one or more of the above-mentioned limitations of prior art arrangements.

It is another object of the invention to provide a superregenerative receiver for receiving modulated carrier-frequency wave signals and having an improved fidelity characteristic.

In accordance with the invention, a superregenerative receiver for receiving modulated carrier-frequency wave signals comprises a regenerative oscillatory circuit and means for supplying to the oscillatory circuit a periodic quench voltage to provide superregeneration. The applied quench voltage has a frequency which islow with reference to the carrier frequency of the signal to be received and high with reference to the highest modulation frequency thereof to be translated. The receiver includes means for deriving from the regenerative oscillatory circuit an output signal having desired signal components which represent modulation components of the received signal and having undesired signal components of frequencies harmonically related to the quench frequency. Additionally, there is included in the receiver frequency-selective signaltranslating means having maximum attenuation at frequencies corresponding to predetermined harmonics of the quench frequency. This lastnamed means is utilized for translating the output signal derived from the oscillatory circuit and for suppressing therefrom at least a selected one of the undesired signal components without substantially distorting the desired signal compoand control electrodes.

3 nents to derive a second signal including the desired signal components. The receiver is also provided with means responsive to the second signal for utilizing the desired signal components.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description-taken in connection with the accompanying Referring now more particularly to the drawings, there is represented in Fig. 1 a superregenerative receiver having a linear mode of operation for receiving modulated carrier-frequency wave signals. Forlconvenience of explanation, the receiver may be considered as a component of a radio locating system in which directionfinding information is received. as pulse modulation of a carrier-frequency wave signal and reproduced on a cathode-ray tube. The receiver comprises a regenerative oscillatory circuit including a vacuum tube I having anode, cathode Tube I0 has a control electrode-cathode circuit which includes a 'frequency-determining circuit M, an oscillation generator I2, and a source of bias voltage Ec. Frequency-determining circuit H is provided by a parallel combination of an adjustable inductor I3 and a condenser C shown in broken-line construction since it may be comprised in whole, or in part, of the distributed capacitance ofeinductor l3, the interelectrode capacitance of the control electrode and cathode of tube I0, as well as other stray capacitance effects associated with.

inductor l3. The tube ||l'has an anode-cathode circuit including an inductor l4 and a source of space current Eb. Inductors l3 and M are inductively coupled, as indicated by M1, providing a voltage feed-back path from the anode-cathode to the control electrode-cathode circuit of tube H) for the purpose of sustaining oscillations. The value of bias voltage supplied from source Ec is selected normally to block oscillations in the described regenerative circuit,

Oscillation generator l2 comprises means for supplying to the regenerative circuit a periodic quench voltage of such magnitude as to overcome the blocking voltage Ec at a predetermined point in positive half cycles in order to provide superregeneration. The quench voltage maybe of sinusoidal wave form having a frequency which is low with reference to the operating frequency of the regenerative circuit and the carrier frequency of the signal to be received. Also, the quench frequency is preferably high with reference to the highest modulation frequency component, of any received signal, to be translated.

The receiver includes means, consisting of a detector system, for deriving from the regenerative oscillatory circuit an output signal which has desired signal components representing modulation components of the received signal, as well as undesired signal components resulting from the quenching action and having frequencies harmonically related to the quench fre- 4 n'i quency. This detector system comprises a diode detector 20 and a load circuit provided by an inductor 2| and a parallel combination of a load resistor 22 and a carrier-frequency by-pass condenser 23. The detector system is coupled to the regenerative oscillatory circuit by Way of an inductive coupling, indicated by M2, between inductors-I3 and 2|. i

There is coupled to the load circuit of the described detector system a frequency-selective signal-translating means 30 having maximum attenuation at frequencies corresponding to predetermined harmonics of the quench frequency. This means is included in the receiver for translating the output signal of the regenerative circuit, as derived in the detector system, and for suppressing therefrom at least one of the unde sired quench-frequency signal components without substantially distorting the desired signal components to derive a second signal which includes the desired signal components, Unit 30 includes an amplifier 3|, the input circuit of which is coupled to the load circuit of the detector system. A pair of series-resonant trap circuits are connected in shunt relation to the input circuit of amplifier 3|. One such trap consists of an inductor 32 and a series-connected condenser 33, while the other is provided by an inductor 34 and a series-connected condenser 35. The first of these traps is resonant, preferably, at a frequency corresponding to the first harmonic, or fundamental, of the quench frequency, while the other is resonant at the second harmonic of "the quench frequency.

The receiver also includes means responsive to the above-mentioned second signal derived in unit 30 for utilizing the desired signal components thereof which represent modulation of the received signal. This means, in the illustrated embodiment, consists of an image-reproducing device 40 having an input circuit coupled to the output circuit of amplifier 3|. The image-reproducing device may comprise a conventional cathode-ray tube for producing a visual pattern of the wave form of the signal applied to its input circuit. It will be understood that device 40 includes a variable-frequency horizontal sweep-signal source for controlling the horizontal traverse of the electron beam of the cathode-ray tube and a vertical deflecting system responsive to the signal output of amplifier 3| for. deflecting the electron beam vertically in accordance with the wave form of the applied signal.

An antenna-ground system 50 including an inductor 5| is utilized for receiving modulated carrier-frequency wave signals to be translated in the receiver. The antenna-ground system is inductively coupled to the regenerative oscillatory circuit, as indicated by M3, between inductors l3 and 5 I.

In considering the operation of the described tions generated in the circuit of tube I 0 in quench cycles which occur within the duration of the tected signal output having the wave form of curve 0. The time constant of resistor 22 and condenser 23 in the load circuit of diode 20 causes the detected signal output. as derived across resistor 22, to havea saw-tooth wave form shown by curve d. This signal, after amplification in unit 30, isapplied to the input circuit of imagereproducing device 80 and a signal pattern corresponding to the wave form of the applied si al is produced.

From a comparison of curve (1 with the modulation envelope of curve a, it is evident that the signal-pattern produced is not a faithful representation of the modulation components of the received pulse. This results, in part, from the frequency-response characteristic of the detector load circuit for the assumed condition. This characteristic, shown by broken-line curve 1:. of Fig. 3, is such that in addition. to desired signal components, which represent modulation of the received signal, undesired signal components attributable to the quenching action are derived in the load circuit of the detector. In this connection it will be noted that the response characteristic is fairly fiat over a range extending 'from zero to approximately one-half the quench frequency .fq, a range which includes all of the desired signal components. One such component, namely the zero-frequency or direct current component, having a wave form which closely approaches the modulation wave form of the received pulse, is represented in curve e. It will also be noted from curve h that undesired signal components of appreciable amplitude and having frequencies equal to first and second harmonics of the quench frequency are derived in the load circuit of the detector. These signal components are represented by curves f and g, respectively,

and are largely responsible for the discrepancies between the wave form of curve d and the modulation of the received signal. Of course, other high-order quench-frequency signal components are present in the signal output of the detector but they are omitted from the drawings for the sake of simplicity.

Considering now the effect of unit 30' on the described response of the receiver, reference is made to full-line curve a of Fig. 3. This curve illustrates the frequency-response characteristic of the input circuit of amplifier 3|. It will be noted that traps 32, 33 and 34, 35 cause unit 30 to have maximum attenuation for signals harmonically related to the quench frequency. Specifically. these traps are eifectiveto suppress from the output signal of the detector system, as it is translated through unit 30, those undesired signal components of frequencies equal to the first and second harmonics of the quench frequency. This suppressing action, beingaccomplished by means of frequency-selective trap circuits, causes substantially no phase distortion of the desired signal components. Consequently, the output signal of unit 30, which has been defined above as a second signal, includes the desired signal components and is substantially free of the low-order quench-frequency signal components: Since those undesired signal components having frequencies which correspond to" 'be neglected, this second signal, derived in unit 30 and applied to the input circuit of image-' reproducing device 40; has a wave form which closely approaches that of curve e in Fig. 2. The resulting pulse pattern produced on the screen of device 40 has substantially, the same wave form and represents the modulation of the re ceived signal with relatively high fidelity. Therefore, the direction-finding information conveyed as pulse modulation of the received signal may readily be obtained from observation of the produced signal pattern.

Certain advantages of the described receiver arrangement over those of the-prior art mentioned above are clearly demonstrated by its frequency-response characteristic, curve 7'. For example, it will be evident that (1) the receiver has a substantially uniform response over a frequency range including all of the desired modulation components of a received signal; (2) the undesired quench-frequency signal components are suppressed from the receiver output signal; and (3) the receiver circuit has a gradual cutoff characteristic, required to avoid phase distortion of the derived modulation components of the received signal. These factors all contribute to produce a fidelity in the described receiver which surpasses that heretofore attainable with receivers of the superregenerative type.

In Fig. 4 there is represented a modification of the frequency-selective signal-translating means utilized in deriving the above-mentioned second signal from the output signal of the detector system. In this modified form, the frequency-selective signal-translating means 60 comprises a vacuum-tube repeater circuit including a vacuum tube 6| having an input circuit coupled across resistor 22 of the detector system. A pair of parallel-resonant trap circuits are included in the cathode circuit of tube 8!. One trap consists of a, parallel arrangement of an inductor'. 62 and a condenser 63 associated with the cathode of tube 6| through an adjustable tap 64. The other trap likewise comprises a parallel combination of an inductor 65 and a condenser 66, and is connected in the cathode circuit through a tap 8T. Each trap is individuallyresonant at a different frequency corresponding to apredetermined harmonic of the quench frequency. Preferably, the resonant frequency of termine the degree of selectivity of the trap circuitsand the over-all frequency-response characteristic of signal-translating means 60.

Instead of utilizing trap circuits in the manner indicated in units 30 and 60 of Figs. 1 and 4, respectively, the undesired quench-frequency signal components of the output signal of the detector system may be suppressed through a timedelay filter network, such as represented in unit 10 of Fig. 5-. This unit comprises a series of section 13.

misson-line section 15 is coupled to the output cascaded vacuum-tube amplifying circuits, only two of which are illustrated in the drawings. The first of these stages includes a vacuum tube ll having an input circuit coupled to resistor 22 of the detector system and having an output circuit coupled to the next succeeding stage including tube I2. A time-delay reflecting-filter network. in the form of an open-circuited transmission-line section 13, is coupled to the output circuit of amplifier 1| and terminated at its input terminals by an impedance l4. Impedance 14 is selected of such value that this impedance, plus the impedance contributed by the anodecathode circuit of amplifier H, constitutes the image or surge impedance of transmission-line Likewise, .an open-circuited transcircuit of amplifier I2 and is terminated at its input terminals by its image impedance 16. Transmission-line sections I3 and 15 are selected to have such effective electrical lengths as to delay a-signal applied thereto for a predetermined period, as will be described presently.

In considering the operation of the Fig. 5 embodiment, reference is made to Figs. 6a-6f, inclusive. The curve of Fig. 6a represents a single pulse of a received pulse-modulated carrier-frequency wave signal. The curves of Fig. 6?) represent, the following components of the resulting output signal derived by detector 20: (1) the direct current component, curve e, and (2) the undesired signal component having a frequency corresponding to the first harmonic of the quench frequency,.'curve f. The signal represented by Fig. 6b is applied to the input circuit of amplifier II and is translated to the output circuit thereof where it is applied to the input terminals of transmission-line section 13, For convenience of illustration, the polarityreversal within the am- 'plifying stage has been neglected. Due to the fact that the remote terminals of the transmission-line section are open circuited, and electrical wave which is the image of the applied .wave is reflected therefrom and appears, after a predetermined delay, across the input terminals of the line. Transmission-line section 13 has an electrical length corresponding substantially to a delayed and undelayed signals present in the output circuit of amplifier H are effectively combined across impedance 1 4, producing a resultant signal represented-by the curves of Fig. 611. Due to the prescribed delay period, undesired signal components having frequencies that correspond to the odd harmonics of the quench frequency are substantially eliminated from this resultant signal. The elimination of such undesired components causes that signal component. curve 9,

having a frequency equal to twice the quench frequencyto be the predominant undesired component in the resultant signal of Fig. 6d. This signal is, in turn. translated by amplifier 12 where a similar delaying and. combining process takes place. In this case, however, transmissionline section 15 has an electrical length equal to an eighth-wave length of the quench frequency. The combining of the delayed signal of Fig. 6e and the undelayed signal of Fig. (id in the output circuit of amplifier 12 produces the resultant sig-' nal of Fig. 6) from which undesired signal components which have a frequency corresponding to twice the quench frequency are effectively sup- 8 pressed. Also, all signal components having frequencies of twice the oddharmonics of the quench'frequency are suppressed by the combining step in amplifier l2. Curve s of Fig 61 represents the signal applied to the image-reproducing device 40 from unit Ill. The wave form of this signal closely approaches the modulation envelope of the received signal.

In describing the several modifications of the invention, mention has been made of removing those undesired signal components which have frequencies equal to the first and second harmonics of the quench frequency, In actual installations it is found that the removal of such undesired components is sufficient to produce a reasonablyaccurate pictorial representation of the desired modulation components of the received si nal. If desired, others of the undesired quenchfrequency signal components may be selectively eliminated. Theoretically, at least,'an improved result may be obtained by multiplyingthe number of trap circuits utilized in the frequencyselective units 30 and 60 of Figs. 1 and 4, respectively. Likewise, an improved result may be obtained with the Fig. 5 embodiment by increasing the number of delaying and combining steps. For example, by including four cascaded amplifying stages in unit 10, all undesired signal components up to and including those which have a frequency corresponding to the eighth harmonic of the quench frequency may'be eliminated. The components eliminated in the successive stages and the time delays involved in in the following table:

Delay of filter network (in fractions of quenchfrequency Wave length) Step No.

Z gza The time-delay filter arrangements of Fig. 5 may take any of a variety of forms. For example, these arrangements may comprise a low-pass filter of an appropriate number of sections; wound or loaded lines; open-wire parallel-conductor'lines; or an equivalent parallel group of series-tuned trap circuits.

It will be understood that the invention is subject to a general application and is not to be limited to the reception ofpulse-modulated carrier-frequency wave signals, as particularly described above. In the reception of any modulated carrier-frequency wave signal, undesired quench-frequency components are introduced by the quenching action and may be suppressed through the use of arrangements of the type disclosed. Also, it will be apparent that imagereproducing device 40 may be replaced by any suitable utilizing circuit for utilizing the derived signal components of received signals.

In addition to providing high fidelity in a superregenerative receiver, the described invention is "particularly useful in connection with a wave-signal transponder system of the regenerative type. By wave-signal transpondor system is meant a wave-signal translating system including a receiver and a transmitter so arranged that a predetermined reply is transmitted in' type, it is common practice toinclude a control arrangement for controlling the sensitivity thereof. Such a control arrangement may derive a gain-control voltage in response to the noisesignal components included in the output signal of the receiver obtained during intervals when no desired signal is being received. In such a case,

a received continuous-wave signal normally causes the transmitter to send out a continuous signal for utilizing said desired. signal composuccession of answer signals, which is an undesirments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is cla med is: I

1. A superregenerative receiver for receiving prising, a regenerative oscillatory circuit, means for supplying to said circuit a period c quench voltage to provide superregeneration, said quench voltage having a frequency which is low with reference to the carrier frequency of the signal to be received and high with reference to the highest modulation frequency thereof to be translated, means for deriving from said regenerative oscillatory circuit an output signal having desired signal components representing modulation components of said received signal and having undesired signal components of frequencies harmonically related to said quench frequency, frequencyselective signal-translating means having maxi mum attenuation at frequencies corresponding to predetermined harmonics of said quench frequency for translating said output signal and for suppressing therefrom at least a selected one of said undesired signal components without substantially distorting said desired signal components 'to derive a second signal including said desired signal components, and means responsive to said second signal for utilizing said desired signal components.

2. A superregenerative receiver for receiving modulated carrier-frequency wave signals comprising, a regenerative oscillatory circuit, means for supplying to said circuit a periodic quench voltage to provide superregeneration, said quench voltage having a frequency which is low with reference to the carrier frequency of the signal to be received and high with reference to the highest modulation frequency thereof to be translated, means including a detector system. for deriving from said regenerative oscillatory circuit an output signal having desired signal components representing modulation components of said received signal and having undesired signal components of frequencies harmonically related to said quench frequency, frequency-selective signaltranslating means having maximum attenuation at frequencies corresponding to predetermined harmonics of said quench frequency for translating said output signal and for suppressing therefrom at least a selected one of said undesired signal components without substantially dismodulated carrier-frequency wave signals com- 10 torting said desired signal components to device a second signal including said desiredi signal components, and means responsive to'said second nents.

3. A superregenerative receiver for receiving modulated carrier-frequency wave. signals comprising, a regenerative oscillatory circuit, means for supplying to said circuit a periodic quench voltage to provide superregeneration,-said quench voltage having a frequency which is low with reference to the carrier frequency of the signal to be received and high with reference to the highest modulation frequency thereof to be translated, means for deriving from said regenerative oscillatory circuit an output signal having desired signal components representing modulation components of said received signal and having undesired signal components of frequencies harmonically related to said quench frequency, frequencyselective signal-translating means having maximum attenuation at frequencies corresponding to predetermined harmonics of said quench frequency for translating said output signal and for suppressing therefrom at least undesired signal component having a frequencycorresponding to the first harmonic of said quench frequency without substantially distortin said desired signal components to derive a second signal including said desired signal components, and means responsive to said second signal for utilizing said desired signal components.

4. A superregenerative receiver for receiving modulatedcarrier-frequency wave signals comprising, a regenerative oscillatory circuit, means for-supplying to said circuit a periodic quench voltage to provide superregeneration, said quench for suppressing therefrom undesired signal components having frequencies corresponding to said predetermined harmonics of said quench frequency without substantially distorting said desired signal components to derive a second signal including said desired signal components, and means responsive to said second signals for utilizing said desired signal components.

5. A superregenerative receiver for receiving modulated carrier-frequency wave signals comprising, a regenerative oscillatory circuit, means for supplying to said circuit aperiodic quench voltage to provide superregeneration, said quench voltage having a frequency which is low with reference to the carrier frequency of the signal to be received and high withreference to the highest modulation frequency therof to be translated, mean forderiving from said regenerative oscillatory circuit an output signal having desired signal components representing modulation components of said received signal and having undeselective signal-translating means including at prising, a regenerative oscillatory circuit, means for supplying to said circuit a periodic quench voltage to provide superregeneration, said quench voltage having a frequency which is low with reference to the carrierfrequency of the signal to be received and high with reference to the highest modulation frequency thereof to be translated,

means for deriving from said regenerative oscillatory circuit an output signal having desired signal components representing modulation components of said received signal and having undesired signal components of frequencies harmonically related to said quench frequency, a vacuum-tube repeater circuit including at least one trap circuit resonant at a frequency corresponding to a predetermined harmonic of said quench frequency for translating said output signal and for suppressing therefrom. undesired signal components having a frequency corresponding to said predetermined harmonic of said quench frequency without substantially distorting said desired signal components to derive a second signal including said desired signal components, and means responsive to said second signal for utilizing said desired signal components.

'7. A superregenerative receiver for receiving modulated carrier-frequency wave signals comprising, a regenerative oscillatory circuit, means for supplying to said circuit aperiodic quench voltage to provide superregeneration, said quench voltage having a frequency which is low with reference to the carrier frequency of the signal to be received and high with reference to the highest modulation frequency thereof to be translated, means for deriving from said regenerative oscillatory circuit an output signal including desired signal components representing modulation components of said received signal and undesired signal components having frequencies harmonically related to said quench frequency, means for delaying said output signal for a period substantially equal to an odd-integral multiple of onehalf period of a predetermined harmonic of said quench frequency without appreciably changing the wave form of the delayed signal and for combining the delayed with the undelayed output signal to develop a resultant signal which includes said desired signal components and which is substantially free of said undesired signal components having a frequency corresponding to said predetermined harmonic, and means responsive to said resultant signal for utilizing said desired 6 signal components.

8. A superregenerative receiver for receiving modulated carrier-frequency wave signals comprising, a. regenerative oscillatory circuit, means for supplying to said circuit a periodic quench voltage to provide superregeneration, said quench voltage having a frequency which is low with reference to the carrier frequency of the signal to be received and high with reference to the highest modulation frequency. thereof to be translated, means for deriving from said regenerative oscillatory circuit an output signal including desired signal components representing modulation components of said received signal and undesired signal components having frequencies harmonically related to said quench frequency, means including a time-delay filter for delaying said output signal for a period substantially equal to an odd integral multiple of one-half period of a predetermined harmonic of said quench frequency without appreciably changing the wave form of the delayed signal and for combining the delayed with the undelayed output signal to develop a resultant signal which includes said desired signal components and which is substantially free of said undesired signal components having a frequency corresponding to said predetermined harmonic, and means responsive to said resultant signal for utilizing said desired signal components.

9. A superregenerative receiver for receiving modulated carrierfrequency wave signals comprising, a regenerative oscillatory circuit, means for supplying to said circuit a periodic quench voltage to provide superregeneration, said quench voltage having a frequency which is low with I reference to the carrier frequency of the signal to be received and high with reference to the highest modulation frequency thereof to be translated, means for deriving from said regenerative oscillatory circuit an output signal including desired signal components representing modulation components of said received signal and undesired signal components having frequencies-harmonically related to said quench frequency, means including a time-delay reflecting-filter network for delaying said output signal fora period substantially equal to an odd-integral multiple of onehalf period of a predetermined harmonic of said quench frequency without appreciably changing the wave form of the delayed signal and for combining the delayed with the undelayed output signal to develop a resultant signal which includes said desired signal components and which is substantially free of said undesired signal components having a frequency corresponding to said predetermined harmonic, and means responsive Y The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,226,657 .Bly Dec. 31, 194.0 1,869,870 Stevenson Aug. 2, 1932 2,174,963 Braaten Oct. 3, 1939 2,230,108 Gerhard Jan. 28, 1941 

